Chemical-to-electrical conversion technology continues to be researched, as the demand increases for higher fuel efficiency. The technical approaches regarding electrochemical conversions are numerous. Moreover, the device applications are also many. For example, electrochemical cells may be used as a NOx decomposing means, wherein the cell is used as a purifier for exhaust gases from an automobile or an electric power-generating apparatus. Moreover, the electrochemical cells may be used for cogeneration for heating domestic hot water together with electrical power.
In particular, solid oxide fuel cells (SOFC) and the derivative technologies are efficient electrochemical cells which can be used for such purposes. Solid oxide fuel cells with membranes formed by extrusion have been used in stationary but not mobile chemical-to-electrical conversions. In one approach, solid oxide fuel cells are comprised in a stationary cogenerator system, wherein a plurality of elongated tubular SOFCs are used to supply electrical power and domestic heating, as described in the referenced publication by T. Alston, K. Kendall, M. Palin, M. Prica, and P. Windibank, entitled "A 1000-cell SOFC Reactor for Domestic Cogeneration," published in the Journal of Power Sources, volume 71, pp. 271 through 278, 1998. In this stationary use, the long cantilevered tubes are not subjected to vibration. In another approach, a solid oxide fuel cell derivative NOx decomposing cell with a honeycomb structural body is formed by integrating at least one dense solid electrolyte body and at least two dense interconnects, as described in referenced patent document, U.S. Pat. No. 6,025,084. In this approach, electrodes are formed on walls of channels extending through the honeycomb structural body. Such a honeycomb structural body may be used as a NOx decomposing cell disposed in the exhaust system of a vehicle. Related honeycomb structures have been used as supports for catalytic exhaust gas treatment and can tolerate the automotive vibration environment. However, the honeycomb structure wastes material and the accompanying mass that are not actively employed in the electrochemical conversion. High power density per unit of conversion system mass is important to designers in the automotive industry, who seek ways to reducing weight while maintaining and increasing overall chemical-to-electrical efficiency.
Although elongated tubular solid oxide fuel cells have been effectively used in stationary systems, the geometrical structure of such SOFC cannot be effectively used in a variable vibration environment such as a vehicle in which vibration across a wide range of frequencies is anticipated to be present during routine operation. In such an environment, the cells will at some point begin to vibrate in resonance at which time the amplitude of the vibration will increase greatly with adverse consequences, such as breaking at a point of connection or at impact with other tubes. For example, when encountering a number of bumps or other irregularities of pavement on which it travels, a vehicle may experience large amplitude vibrations within the range of about 20 to 600 Hertz which represents a range which likely includes the tubular design resonance frequencies.
Although honeycomb structural bodies have been used to withstand the vibration in the exhaust systems of vehicles, the power density of the solid oxide fuel cells based on honeycombs is decreased, increasing the total weight and cost of the material in the chemical-to-electrical conversion system. Many honeycomb structures have geometric structures resulting in much unused material and thus less power density. For example, a honeycomb structure may include a matrix of solid electrolyte sub-bodies, each of which is separated from one another by dense interconnects. The interconnects disposed within serve only to connect bodies for aggregate voltage and do not contribute to the electrochemical conversion, resulting in added weight and less power density of the honeycomb as a whole.